Interception patters of solar radiation in vineyards with and without plastic covering/Padroes de interceptacao de radiacao solar em vinhedos com e sem cobertura plastica

The study aimed to evaluate interception patterns of photosynthetically active radiation (PAR) in vineyards (Vitis vinifera cv. 'Moscato Giallo'), with and without plastic covering over the vegetative canopy. An experiment was carried out in Flores da Cunha, Rio Grande do Sul state, Brazil (29 °06'S, 51 °20'W, 541 m) during the 2005/2006 growing season. It comprised uncovered and covered rows of plants by using a transparent 160 Lim thick plastic film (low density polyethylene). Continuing measurements of PAR were taken at different levels of the canopy in both treatments. The leaf area index (LAI) was determined by a non-destructive method along the crop cycle, and regression models relating LAI to the accumulated degree-days were adjusted. Regression models were also adjusted in order to estimate the intercepted PAR as function of LAI by covered and uncovered vineyards. The plastic covering over the vineyard promoted an increment of 12% for the interception efficiency of PAR. The covered vineyard showed a lower extinction coefficient for PAR than in open sky. Index terms: grapes, plasticulture, photosynthetically active radiation, microclimate. O trabalho teve por objetivo avaliar padroes de interceptacao da radiacao fotossinteticamente ativa (RFA) em vinhedos de 'Moscato Giallo', com e sem cobertura plastica sobre o dossel vegetativo. O experimento foi conduzido no municipio de Flores da Cunha, na "Serra Gaucha" (29 °06'S, 51 °20'W, 541 m), na safra de 2005/2006. Consistiu de fileiras de plantas descobertas e cobertas com filme de polietileno de baixa densidade transparente com 160Lim de espessura. Foram feitas medicoes continuas de RFA em diferentes alturas do dossel, nos dois sistemas. O indice de area foliar (IAF) foi determinado por metodo nao destrutivo, tendo-se ajustado modelos relacionando IAF com graus-dia acumulados. Tambem foram ajustados modelos relacionando a eficiencia de interceptacao de RFA com IAF, nos vinhedos cobertos e descobertos. A cobertura plastica promoveu aumento de 12% na eficiencia de interceptacao da radiacao pelo vinhedo. O vinhedo coberto apresentou menor coeficiente de extincao de RFA que em ceu aberto. Termos para indexacao: Videira, plasticultura, radiacao fotossinteticamente ativa, microclima.